In the past, various attempts have been made to provide a regulating mechanism for the hydraulic pressure of a vehicular brake mechanism. The purpose is to decrease the pressure on a hydraulic brake when a sensor detects that the wheel locks up and thus risks skidding on the road surface. Such attempts have generally been made by providing means for pumping fluid away from the operating or slave cylinder of the brake on the locked wheel.
Examples of prior art anti-locking braking systems include:
Lester et al, U.S. Pat. No. 3,544,171; PA1 Skoyles, U.S. Pat. No. 3,724,914; PA1 Gfeller, U.S. Pat. No. 3,752,268; PA1 Baynes et al, U.S. Pat. No. 4,046,427. PA1 a housing with an inlet and an outlet for hydraulic fluid; PA1 an inlet chamber and an outlet chamber, fluid connection between these chambers being controlled by valve means; PA1 means for opening or closing the valve means comprising a rotable cam in contact with said valve means; PA1 and means for modulating the pressure within said outlet chamber when the fluid connection between the inlet and outlet chambers is cut off. PA1 at least one pressure regulator as described in the preceding paragraph; PA1 at least one hydraulic actuating means, each arranged to apply a brake to a moving object; PA1 at least one sensor, each sensor at or adjacent each moving object; PA1 a hydraulic pressure generator adapted to supply hydraulic fluid under pressure to said hydraulic actuating means to apply said brakes; PA1 and at least one of said pressure regulators between said pressure generator and said actuating means to regulate the hydraulic fluid pressure reaching the actuating means in response to signals from said sensor(s).
Lester et al discloses the use of a servo controlled piston to move a cylinder into or out of a chamber to vary the chamber volume and hence decrease the braking pressure when skidding occurs.
Baynes discloses an inertial cam which is responsive to the skidding of a rear wheel, and requires a complex fly-wheel arrangement to regulate the braking pressure.
Skoyles teaches the use of a rotary cam to actuate a pump thereby increasing braking pressure after the brake pressure has been released.
Gfeller describes a complex system for controlling the braking pressure on a mountain railway.
Such regulators have, however, been expensive to construct and install.
Their complexity and need for servos on pumps increase the size and weight of the entire braking system.